Water-dispersable copolymers and their use as pigment dispersant in waterbased coating compositions are well known in the art. For example, U.S. Pat. No. 5,231,131 describes aqueous pigment dispersants based on graft copolymers comprising a hydrophobic polymeric backbone, containing hydrophobic monomers, and side chains of hydrophilic macromonomers. Particularly useful graft copolymers have a backbone of polymerized methylacrylate, butylacrylate, ethylacrylate and optionally acrylic acid or acryl amido methylpropane sulfonic acid.
EP 1 197 537 further discloses aqueous pigment dispersing resins based on graft copolymers comprising macromonomers obtained from methacrylic acid esters and styrene and optionally methacrylic acid and a polymeric backbone based on monomers comprising a monomer with ionic functional groups selected from amino, quarternary ammonium salt and sulfonic acid groups and comprising a monomer having polyoxyalkylene chains.
All those already known pigment dispersants have a common disadvantage. Pigment dispersions based on the already disclosed graft copolymers lead to coatings with insufficient intensity of coloration and in particular insufficient jetness in case of black coatings.
Therefore, it is an object of the present invention to provide pigment dispersions with high wetting properties and dispersing stability which can be used in preparing pigmented coating compositions, in particular coating compositions pigmented with black pigments, which lead to coatings of high color strength and in particular to coatings with high jetness.